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Archive for October, 2015

Nowhere Near Room Temp Superconductors

Friday, October 30th, 2015

On-chip metal interconnects limit IC speed in many advanced design today, and with signal delay proportional to the product of the resistance (R) of wires and the capacitance (C) of dielectric insulation, wires with R lower than that of copper (Cu) metal would significantly improve IC performance. We know of superconductors—materials with zero resistance to electrical current flow—but only at “critical temperature” (Tc) well below 77°K, and so there has been an ongoing quest by scientists to find a material with Tc above room temperature of 298°K.

Sadly, after 4 years and nearly 1000 materials tested, a team of 6 Japanese research groups led by Hideo Hosono from the Tokyo Institute of Technology found no room temperature superconductors. They did find 100 previously unknown superconductors with Tc <56°K, and they published crystal structures and phase diagrams of all materials studied to help other researchers avoid now known dead-ends (DOI: 10.1088/1468-6996/16/3/033503).

Other researchers continue to explore the possibilities of using one-dimensional (1D) carbon-based materials such as carbon-nano-tubes (CNT) or graphene as on-chip conductors. So far, there are extreme difficulties in controlling the growth of such 1D structures within interconnect patterns, and additional challenges with forming ohmic contacts between CNT and Cu lines across billions of connections in a modern IC. More science is seemingly needed to find new paths before the engineers can explore those paths to find better solutions. Meanwhile…for the next few years at least…expect Cu metal to be the continued choice for nearly all multi-level metal interconnects on chip.

—E.K.

EUV Cost at 1000 Daily Exposures

Monday, October 26th, 2015

On October 14, 2015, ASML Holding N.V. (ASML) published its 2015 third-quarter results:  Q3 net sales of €1.55 billion with gross margin of 45.4% (in line with guidance), and guided Q4 2015 net sales at approximately €1.4 billion and a gross margin of around 45%. Due to mismatched financial analyst expectations, Bloomberg reported that ASML’s stock price dropped ~7% in a single day of trading, despite the company also reporting upgrades to both the TWINSCAN NXT 193nm-immersion (193i) and the NXE Extreme Ultraviolet (EUV) tools. In particular, a new record of 1000 wafer exposures in a single day was set by one EUV tool.

The science of controlling the 13.54nm wavelength electromagnetic radiation that we like to call “Extreme Ultra-Violet” or “EUV” (instead of the colloquial scientific term “soft x-ray”) is inherently challenging. The engineering of EUV Lithography is not just challenging but bordering on inherently impossible:  from exploding tin plasma source, to all-reflective lenses that absorb energy, to the trade-offs in mask pattern protection. The team at ASML working on the exposure tool—along with the different specialist organizations still working on improved sources, masks, and resists—deserve the industry’s unwavering admiration for the important work they do every day.

In a prepared statement, ASML President and Chief Executive Officer Peter Wennink said, “We have proven the capability both to expose 1,000 wafers per day and, in a manufacturing readiness test, to expose 15,000 wafers in four weeks. We have also achieved a four-week average availability of more than 70 percent  at multiple customer sites. The first shipment of our fourth-generation EUV lithography system, the NXE 3350B, is in progress, with two more expected to ship in Q4.”

Still, progress along desired EUV roadmaps continues to be slow, and the competitive target shifts when the 193i exposure tool gains a 10% throughput improvement to 275 wafer-passes/hour (wph). When the 193i tool gains a 30% overlay improvement, that means double-patterning based on litho-etch-litho-etch (LELE) process flows gain in pattern fidelity. Since ASML provides both technologies, delays in orders for EUV just means more sales of 193i tools.

Let’s play with the numbers here…275 wph x 20 hours x 30 days = 165k wafer-passes/month for the NXT:1980. The NXE:3350B can current handle 15k wafer-passes/month. So even if the tools were equally priced, just based on tool depreciation each EUV exposure today costs >10x that of a 193i exposure, which is why pitch-splitting multi-patterning 193i continues to dominate.

—E.K.